Spark plugs of the pre-igniting chamber type



Ju'fiy 15%, WW 5. SSZELAGYE 3,333,975

SPARK PLUGS OF THE PRE-IGNITING CHAMBER TYPE Filed Aug. 16, 1966 2 Sheets-Sheet l Inventor Asrm/v 52/4 46 y/ ByW 1LJWW 511115? 38, 39%? I. SZILAGYI SPARK PLUGS OF THE FEE-IGNITING CHAMBER TYPE 2 Sheets-Sheet 2 Filed Aug. 16, 1968 Aiiomeys United States Patent 3,331,976 SPARK PLUGS OF THE PRE-IGNITING CHAMBER TYPE Istvan Szilagyi, 8 Nagymezo utca, Budapest, Hungary Filed Aug. 16, 1966, Ser. No. 572,705 Claims priority, applicastion Hungary, Dec. 19, 1962, I 845 Claims. E31. sis-11.5

ABSTRACT OF THE DISCLOSURE gap.

This application is a continuation-in-part of my copending application Ser. No. 329,645, filed Dec. 11, 1963, now abandoned.

This invention concerns spark plugs of the pre-igniting chamber type.

In hitherto known spark plugs of the self-cleaning type a central electrode is embedded for the major part of its length in an insulating body and protrudes therefrom to a small extent into the combustion chamber of the internal combustion engine in which the spark plug is to be used. As a result, the insulating body, together with the central electrode, becomes incandescent in operation and the impurities such as soot deposited thereon are burnt ofi thereby avoiding short-circuiting of the current leakage paths. This simultaneous incandescence, usually at about 800850 0, determines the so-called thermal value of the conventional spark plugs. However, the incandescent insulating body has no chance to cool down before the next charge of the fuel/ air mixture is introduced into the combustion chamber and so, under certain conditions, undesirable premature ignition may occur.

Moreover, different spark plugs have to be used for engines designed for low speed and high speed operations respectively because of the different thermal values required from the plug.

It is an object of the present invention to provide a spark plug applicable both to low speed/low compression ratio and to high speed/high compression ratio engines in which proper ignition is provided under all conditions and in which the insulating body does not reach incandescence temperature except at the instant of the explosion of the charge.

According to the present invention there is provided a spark plug comprising a ground electrode, a current input electrode electrically separated from said ground electrode, a hollow insulation body arranged between said ground electrode and said input electrode and encompassing a pre-igniting chamber, a central electrode disposed on the inner wall surface of said hollow insulation body, said central electrode being electrically connected to one of said input and ground electrodes to form an extension thereof, there being a spark gap in the current path between said ground and input electrodes adjacent said central electrode. The length of the input electrode and/or the central electrode can be selected so as to predetermine the size and location of the spark gap; and in this sense, the lengths of these members are variable.

The central electrode may be formed entirely of metal- 3,331,976 Patented July 18, 1967 lic net; alternatively it may be formed entirely of a metal layer precipitated on said inner wall surface.

The insulation body may comprise a pair of concentric annular insulation tubes and wherein the central electrode is annular, said central electrode being disposed between, and on the wall surface of, one of said concentric insulation tubes.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view of a spark plug according to one embodiment of the present invention, showing the spark gap in one extreme position thereof;

FIGURE 2 is a view generally similar to that of FIG- URE 1 but showing a second embodiment in which the spark gap is in the other extreme position thereof;

FIGURE 3 is a further sectional view of the invention showing a third embodiment, and

FIGURE 4 is a yet further sectional view showing a fourth embodiment of the present invention.

The same reference numerals indicate identical parts throughout the drawings.

Referring first to FIGURES 1 and 2, there is shown a spark plug having a current input electrode 10 embedded in an insulating shell 11 which has an enlarged head portion 11a. The head portion 11a is located inside the spark plug body 12 which is provided with a bore in the upper portion 12a thereof through which extends the shell 11. A spring 13 is interposed between the upper part of the head portion 11a (as seen on the drawings) and the inner wall of the upper portion 12a of the plug body 12.

The plug body 12 is generally cylindrical and its bottom portion (as seen on the drawings) is threaded to receive a metal housing 15 which serves as a ground electrode and which has threaded internal wall portions to mate with the plug body 12. Observation windows 12b are cut in the plug body 12 which also serve to provide cooling passages for the interior of the plug body.

The housing 15 is also generally cylindrical with an enlarged upper portion surrounding the bottom of the plug body 12 and is formed with an annular shoulder 15a.

The plug body 12 and the housing 15 define an internal space 16 in which is disposed a hollow annular frustoconical insulation body 17. The insulation body 17 is located, by means of upper and lower sealing rings 18, 19 respectively, between the insulating shell 11 and the annular shoulder 15a.

In the embodiment of FIGURE 1 the central electrode is constituted by the lower end 10a of the current input electrode 10. A metallic net 20 is arranged on and in contact with the inner wall of the insulation body 17, extending along the major portion of the length thereof and being in electrical contact with the housing 15 in the region of the annular shoulder 15a. The upper end of the net 2%) is spaced from the lower end 10a of the current input electrode 10 thus defining a spark gap therebetween.

By shortening the length of the screen or net 20 and correspondingly lengthening the current input electrode 10, the position of the spark gap within the insulation body 15 may be varied. This variation introduces a small variation in the thermal value of the plug.

A limiting position is shown in the FIGURE 2 embodiment. Here the net 20 is actually attached to the lower end 10a of the input electrode 10 and the spark gap is formed between the lower end of the net 20 and the upper surface of the annular shoulder 15a. As can be seen in FIGURE 2, the sealing ring 19 has an inner diameter larger than that of either the insulation body 17 or the annular shoulder 15a to facilitate formation of the spark gap.

In both these embodiments, the net 20 is preferably force-fitted on the inner wall of the insulator body 17, which will in this way provide good support against mechanical vibrations. Thus the net 20 may be made of thinner material than would otherwise be possible.

The net electrode 20 provides a central electrode of extremely high surface area/ mass ratio which results in rapid cooling. Moreover, even though the insulation body 17 is a very poor conductor, it is still a better conductor than gases which surround some prior art spark plugs having net electrodes in which these electrodes are not in contact with the insulator body 17.

Furthermore, it in the present construction the centralv electrode were in a space surrounded by gases, the whole volume of the pre-igniting chamber formed by the .internal space within the insulator body 17 would not be utilised so effectively, since it is doubtful whether the fresh mixture, usually at about 6 atmospheres pressure, would penetrate to the full depth of the said space. However, at

an ignition pressure of about 35 atmospheres the present pre-igniting chamber achieves full penetration.

As indicated before, the net 20 will only glow at the moment of ignition when its temperature reaches approxi' mately 1200 C. However, the temperature of the insulator body 17 remains at around 250 C. and this large difference assists in the rapid cooling of the net 20. Thus the net may be quite thin without fear, of being burnt out by the current passing therethrough;

In the FIGURE 1 embodiment the interior space of the insulator body 17 forms a frus-to-conical chamber operating as a pre-igniting chamber in which combustion takes place first. The flame then penetrates therefrom into the combustion chamber of.the engine to ignite the mixture therein. Clearly the ignition of a relatively small volume of fuel/ air mixture is easier than that of a large volume of mixture as is the case where the spark gap is located in the engine combustion chamber proper. This is especially important for low octane operations.

As stated above, windows or slots 1215- are provided in the plug body 12. Apart from assistance with cooling, these windows can also enable a motorist to observe the operation of the sparking plug, and by suitably providing him with a colour chart, he may make some helpful deductions as to the functioning of his engine by observing the colour of the explosion. Thus if he sees a blue flame, the carburetor is providing a correct mixture. A yellowish flame would indicate a too rich mixture whereas a reddish flame would indicate a mixture toodeficient in fuel.

It was indicated above that the net 20 of the FIGURES 1 and 2 embodiments may be made extremely thin. In fact, it was found that, as shown in FIGURE 3, the central electrode can be a metallic layer 21 precipitated onto the inner wall of the insulator body 17 by any suitable method, e.g. cathode sputtering.

Here the layer 21 iselectrically connected to the lower end 1012 of -the input electrode andthe spark gap is formed between the lower end of the layer 21 and the annular shoulder a which projects a small distance inwardly of the sealing ring 19.

Again, in this embodimentalso the position of the spark.

gap could be varied by appropriately lengthening the input electrode 10 and correspondingly shortening the layer 21.-

The central electrode could be heat-insulated even further by arranging it between a pair of hollow, annular, concentric insulator bodies 17a and 17b, which may be cylindrical, as shown in FIGURE 4. The bodies 17a and 17b define a cavity 22 therebetween in which the central electrode is disposed. The central electrode 20 may be a net as in the FIGURES 1 and 2 embodiments, or a precipitated layer as in the FIGURE 3 embodiment. In either necting the lowermost end of the central electrode 20 to the annular shoulder 15a and by interrupting the electrode 20 at some point within the cavity 22. Of course, a corresponding gap would have to be created in the inner insulator body 17b to give access to the spark gap for the mixture in the space 23. The lower part of the insulator body 17b would then have to be secured to the annular shoulder 15a.

The operation of the spark plug is similar in all four embodiment-s. Thus on closing the ignition circuit (not shown) a very large potential diiterence is established across the spark gap which is discharged as a spark.

In all four embodiments the net 20 or the layer 21 can be used as a noise trap resistor as well, if, for example, its resistance is designed to be about 8,000 to 10,000 ohms.

Thus the present invention provides a spark plug in which the central electrode becomes incandescent only momentarily during-the firing of the fuel/airmixture, while the insulating body substantially never incandesces, thereby eliminating the limits set on the heat range or thermal value ofthe spark plug. The prevailing temperature on the insulating body is so low that any-impurities deposited do not cause difiiculty, since they are either dislodged by the mechanical vibrations in the system, or remain below the temperature (approximately 300 C.) at which they begin to conduct electricity to any appreciable extent.

I claim:

1. A spark plug comprising a ground electrode, a current input electrode of variable length electricallyseparated from said ground electrode, a hollow insulation body arranged between said ground electrode and said input electrode and encompassing a pro-igniting chamber, a central electrode of variable length disposed on the inner wall surface of said hollow insulation body, said central 'electrode being electrically connected to one of said input and ground electrodes to form an extension thereof, there being a spark gap in the current path between said ground and input electrodes, the position of the spark gap being variable by varying the lengths of said central and input electrodes.

2. A spark plug according to claim 1 wherein the central electrode is formed entirely of metallic net.

3. A spark plug according to claim 1 wherein the central electrode is formed entirely of a metal layer precipitated on said inner wall surface.

4.- A spark plug according to claim 1 wherein said insulation body comprises a pair-of concentric annular insulation tubes and wherein the central electrode is annular, said central electrode being disposed between, and on the wall surface of, one of said concentric insulation tubes.

5. A spark plug according to claim 1 wherein the central electrodeis electrically connected to said ground electrode and extends along at least the major portion of the length of the hollow insulation body, the sparkvgap being located entirely within the hollow insulation .body and between the central and input electrodes.

6. A spark plug according to claim 1 wherein the central electrode is electrically connected to said input electrode and extends along at least the major portion of the length of the hollow insulation body, the spark gap being rent input electrode electrically separated from saidv ground electrode, a hollow insulation body arranged between said ground electrode and said input electrode and encompassing a preigniting chamber, a central electrode disposed on the inner Wall surface of said hollow insulation body, said central electrode being electrically connected to one of said input and ground electrodes, there being a spark gap in the current path between said ground and input electrodes, the hollow insulation body being of frusto-conical shape the cross section of which decreases uniformly from that end of the spark plug at which, in operation, a fuel/ air mixture enters.

9. A spark plug comprising a ground electrode, a current input electrode electrically separated from said ground electrode, a hollow insulation body arranged between said ground electrode and said input electrode and encompassing a pre-igniting chamber, a central electrode disposed on the inner wall surface of said hollow insulation body, said central electrode being electrically connected to said ground electrode and extending along at least the major portion of the length of the hollow insulation body, there being a spark gap located entirely within the hollow insulation body between the central and input electrodes.

10. A spark plug comprising a ground electrode, a current input electrode electrically separated from said ground electrode, a hollow insulation body arranged between said ground electrode and said input electrode and encompassing a pre-igniting chamber, and a central electrode formed substantially entirely of metal net disposed on the inner wall surface of said hollow insulation body, said central electrode being electrically connected to one of said input and ground electrodes, there being a spark gap in the current path between said ground and input electrodes.

References Cited UNITED STATES PATENTS 1,092,322 4/1914 Witter 313143 2,054,134 9/1936 Mitchel 313-143 2,745,980 5/1956 Smits 313-443 JAMES W. LAWRENCE, Primary Examiner. V. LAFRANCHI, Assistant Examiner. 

1. A SPARK PLUG COMPRISING A GROUND ELECTRODE, A CURRENT INPUT ELECTRODE OF VARIABLE LENGTH ELECTRICALLY SEPARATED FROM SAID GROUND ELECTRODE, A HOLLOW INSULATION BODY ARRANGED BETWEEN SAID GROUND ELECTRODE AND SAID INPUT ELECTRODE AND ENCOMPASSING A PRE-IGNITING CHAMBER, A CENTRAL ELECTRODE OF VARIABLE LENGTH DISPOSED ON THE INNER WALL SURFACE OF SAID HOLLOW INSULATION BODY, SAID CENTRAL ELECTRODE BEING ELECTRICALLY CONNECTED TO ONE OF SAID INPUT AND GROUND ELECTRODES TO FORM AN EXTENSION THEREOF, THERE BEING A SPARK GAP IN THE CURRENT PATH BETWEEN SAID GROUND AND INPUT ELECTRODES, THE POSITION OF THE SPARK GAP BEING VARIABLE BY VARYING THE LENGTHS OF SAID CENTRAL AND INPUT ELECTRODES. 